A wireless broadband network system, such as a long term evolution (LTE), an LTE-advanced (LTE-A), and so on, includes two system modes, i.e., a time division duplex (TDD) system mode and a frequency division duplex (FDD) system mode. Generally speaking, the TDD-LTE and the FDD-LTE can be used to district different system modes.
Either in the LTE system or in the LTE-A system, unsynchronization in timing would lead to bad influence. In a system employing the TDD mode, interference may occur due to different signal directions between base stations or user ends. In a system employing the FDD mode, an enhanced intercell interference coordination (eICIC/Further-eICIC) mechanism adopted for solving co-channel interference problem between a high-power and a low-power base stations in a heterogeneous network system may not be used due to the base stations being unsynchronized with each other. Therefore, timing synchronization is a major subject to the system no matter whether the TDD mode or the FDD mode is adopted.
In a 4G long term evolution (4G LTE) network architecture, telecommunication service providers can solve the problem with respect to the timing synchronization between the base stations by using a global positioning system (GPS) based on protocols, such as a precise time protocol (PTP) defined by the IEEE 1588 standard or a radio-interface based synchronization (RIBS) protocol.
Nevertheless, in a timing synchronization method using the GPS, each base station may meet an accurately timing requirement through satellites; however, the base stations located indoors would be blocked from receiving GPS signals, while the cost would be increased if additional outdoor antennas are installed, which becomes the major problem that indoor type base stations cannot achieve the timing synchronization by using the GPS. On the other hand, in a timing synchronization method employing the IEEE 1588 standard, not only a back-end network has to support the PTP protocol defined by the IEEE 1588 standard, but also a wired network has to be provided with a bidirectional symmetry capability, which causes limitations to its application.
Moreover, a wireless interface synchronization mechanism is proposed in Releases 12 and 13 of the 3rd generation partnership project (3GPP), which is an synchronization mechanism extending the network listening capability originally launched in Release 9. The base stations using the wireless interface synchronization mechanism can perform the timing synchronization between the base stations and coordination and exchange of stratum levels through a backhaul; however, a distance between the base stations using this mechanism cannot be over 500 meters or four stratum levels, which also causes difficulties to the application.